So why not create a die that works like the lee but also pushes the shoulder back so you don't have to fl size?

It's not a collet die, but the Forster Bushing Bump die is one option that's available off the shelf. You can bump the shoulder one or two thousandths, size the neck with a bushing to control neck tension and run it without an expander button. The bushings are cryo treated, so are hard and low friction and I haven't had any problems running the die lubeless (I keep them clean and polished though). It lacks the sliding sleeve of the Redding Competition Bushing die, but I have noticed any worse runout as a result. I don't think it will eliminate the need to FL size occasionally though, since the body size will still increase.